Composite fiber filter comprising nan0-materials, and manufacturing method and apparatus thereof

ABSTRACT

Disclosed herein is a method for manufacturing a composite fiber filter having high efficiency and high functionality, the method comprising: melt-spinning microfiber yarns on a forming rod, which is made of a conductive material, grounded at one end thereof and rotatably driven, using a melt-spinning device, to form on the forming layer a microfiber layer consisting of the microfiber yarns; and electrospinning on the microfiber layer an electrospinnable polymer solution having a given dielectric constant, using an electrospinning device, so as to form on the microfiber layer a nanofiber layers consisting of nanofiber yarns, wherein the microfiber yarns of the microfiber layer and the nanofiber yarns of the nanofiber layer contain silver nanoparticles so as to have an antibacterial function.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a filter unit, and more particularly to an apparatus and method of manufacturing a composite fiber filter having high efficiency, high-functionality and antibacterial activity by combining nanofibers with microfibers.

2. Background of the Related Art

Generally, most microfibers are manufactured through spinning processes such as melting spinning, dry spinning or wet spinning, that is, by extruding and spinning a polymer solution through fine holes by mechanical forces. However, the microfibers manufactured in this manner have a diameter of about 5-500 μm and it is difficult to manufacture nano-scale fibers having a diameter of less than 1 μm. Accordingly, with a filter made of such microfibers, micrometer-sized contaminant particles can be filtered out, but it is in fact impossible to filter out nanometer-sized fine contaminant particles.

Thus, various methods for manufacturing nanometer-sized fibers (nonwoven fabrics) have been developed. Methods for forming organic nanofibers include the formation of nanostructure materials by block segments, the formation of nanostructure materials by self-assembly, the formation of nanofibers by polymerization in the presence of a silica catalyst, the formation of nanofibers by a carbonization process after melt spinning, the formation of nanofibers by electrospinning of a polymer solution or melt, etc.

When a nanofiber filter is produced using the nanofibers thus manufactured, it has a surface area significantly larger than that of a microfiber filter, good flexibility for surface functional groups, and nano-scale pore size, and thus can effectively remove noxious particles or gases.

However, in producing a filter using nanofibers, a very high production cost is incurred and it is not easy to adjust various production conditions. For this reason, it is impossible to produce and distribute the filter made of nanofibers at a relatively low cost.

In manufacturing a filter using nanofibers, problems of differential pressure and filtration efficiency, in addition to the above-mentioned high cost, can occur. If a functional filter, which has a competitive price and, at the same time, solves problems of differential pressure and filtration efficiency and also ensures high efficiency and high functionality, can be developed using a combination of the existing microfiber technology and nanofiber manufacturing technology, it will be highly useful in various industrial fields.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a composite fiber filter having high efficiency, high functionality and antibacterial activity, which comprises a composite of nanofibers and microfibers, as well as an apparatus and method for producing said composite fiber filter.

Another object of the present invention is to provide an apparatus and method by which a composite fiber filter comprising a composite of nanofibers and microfibers can be produced with high productivity.

Still another object of the present invention is to provide a composite fiber filter for water purification, having high efficiency, high functionality and antibacterial activity, as well as an apparatus and method for manufacturing the same.

To achieve the above objects, in one embodiment, the present invention provides a method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is made of a conductive material, grounded at one end thereof and rotatably driven, using a melt-spinning device, so as to form on the forming layer a microfiber layer consisting of the microfiber yarns; and electrospinning an electrospinnable polymer solution having a given dielectric constant, on the microfiber layer, using an electrospinning device, so as to form on the microfiber layer a nanofiber layer consisting of nanofiber yarns.

In the method of the present invention, the polymer resin solution preferably contains self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of the polymer resin. Preferably, polypropylene chips containing silver nanoparticles are melt-spun on a microfiber yarn nonwoven fabric, such that the silver nanoparticles are contained in the microfiber yarn nonwoven fabric.

In another embodiment, the present invention provides a method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is made of a conductive material, grounded at one end thereof and rotatably driven, using a first melt-spinning device, so as to form on the forming rod a first microfiber layer consisting of first microfiber yarns; electrospinning an electrospinnable polymer resin having a given dielectric constant, on the microfiber layer, using an electrospinning device, so as to form on the microfiber layer a nanofiber layer consisting of nanofibers; and melt-spinning microfiber yarns on the nanofiber layer using a second melt-spinning device, so as to form on the nanofiber layer a second microfiber layer consisting of second microfiber yarns having a diameter different from that of the first microfiber yarns, wherein the fiber layers are sequentially deposited on the forming rod.

In still another embodiment, the present invention provides an apparatus for manufacturing a composite fiber filter using nanofibers, the apparatus comprising: a forming rod, which is made of a conductive material and grounded at one end thereof and can be rotatably driven by a driving unit; and one or more melt-spinning devices and electro-spinning devices, which are provided in the vicinity of the forming rod, whereby a microfiber layer consisting of microfiber yarns and a nanofiber layer consisting of nanofiber yarns are alternately and sequentially deposited on the forming rod by melt-spinning from the melt-spinning devices and electrospinning from the electrospinning devices.

In yet another embodiment, the present invention provides a method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is rotatably driven, using a first melt-spinning device, so as to form on the forming rod a first microfiber layer consisting of first microfiber yarns; winding on the first microfiber layer a planar nanofiber nonwoven fabric consisting of nanofiber yarns, which contain silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin, to a given thickness, so as to form on the microfiber layer a nanofiber layer; and melt-spinning microfiber yarns on the nanofiber layer using a second melt-spinning device, so as to form on the nanofiber layer a second microfiber layer consisting of second microfiber yarns having a diameter different from that of the first microfiber yarns, wherein the fiber layers are sequentially deposited on the forming rod.

In yet still another embodiment, the present invention provides a method for manufacturing a composite fiber filter using nanofibers, the method comprising laminating a nanofiber nonwoven fabric on a microfiber nonwoven fabric using an electrospinning process, and then winding the resulting fabric structure in the form of a cylinder to a given thickness so as to manufacture a nanocomposite fiber filter for water purification, wherein nanofibers forming the nanofiber nonwoven fabric contain self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin, and the nanofiber nonwoven fabric has a porosity of 30-70% and a density of 0.1-0.22 g/cm³.

In further still another embodiment, the present invention provides a method for manufacturing a composite fiber filter using nanofibers, the method comprising stacking planar nanofiber nonwoven fabrics alternately with planar microfiber nonwoven fabrics to form a multilayer structure, and then bending the multilayer structure to form a folded cylindrical nanocomposite fiber filter, wherein the nanofiber nonwoven fabric consists of nanofibers containing self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin and has a porosity of 30-70% and a density of 0.1-0.22 g/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing the construction of a composite fiber filer-manufacturing apparatus according to an embodiment of the present invention;

FIG. 2 is a perspective view of a cylindrical composite fiber filter according an embodiment of the present invention;

FIG. 3 is a cross-sectional view of a cylindrical composite fiber filter, which shows an example in which a plurality of nanofiber layers is formed;

FIGS. 4 a and 4 b show TEM analysis images for polyamide (nylon 6)/silver nanofiber yarns;

FIG. 5 shows an EDS analysis image for polyamide (nylon 6)/silver nanofiber yarns;

FIGS. 6 a and 6 b are bar graphs showing the results of antibacterial activity tests conducted using Staphylococcus aurus and Klebsiella pneumonia;

FIG. 7 shows the results of antibacterial zone tests conducted using Staphylococcus aurus and Klebsiella pneumonia;

FIG. 8 is an SEM image photograph showing nanofiber layers deposited on an inner microfiber layer according to an embodiment of the present invention;

FIGS. 9 a to 9 c are SEM image photographs of partial cross-sections, showing that a nanofiber layer and an outer microfiber layer are sequentially deposited on an inner microfiber layer;

FIGS. 10 a and 10 b show the test results of filtration efficiency as a function of particle size in a prior filter and the inventive composite fiber filter; and

FIGS. 11 a and 11 b show the test results of pressure loss as a function of flow rate in a prior filter and the inventive composite fiber filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is noted that like elements throughout the drawings will be denoted by like reference numerals, if possible. Also, the detailed description of known functions and constructions unnecessarily obscuring the subject matter of the present invention will be avoided.

In the present invention, a novel type of highly efficient, highly functional composite fiber filter, which has fine pores and, at the same time, does not cause an increase in pressure, is manufactured by combining a nanofiber nonwoven fabric with microfibers.

FIG. 1 shows the construction of a composite fiber filter-manufacturing apparatus 100 according to an embodiment of the present invention, and FIG. 2 is a perspective view of a cylindrical composite fiber filter 200 manufactured using the composite fiber filter-manufacturing apparatus 100 according to the embodiment of the present invention.

As shown in FIG. 1, the composite fiber filter-manufacturing apparatus 100 according to the embodiment of the present invention comprises a driving unit 4 having a forming rod 2, first and second melt spinning devices 6 and 10, an electrospinning device 8, cold rollers 12 a and 12 b, and a cutter unit 14, and is constructed such that continuous manufacturing through an automated process is possible.

The driving unit 4 drives to rotate the forming rod 2 under the control of a control unit in the composite fiber filter-manufacturing apparatus 100. Also, when a fiber layer formed on the forming rod 2 needs to be moved horizontally, the driving unit 4 projects a piece received in the forming rod 2, under the control of the control unit, such that the fiber layer formed on the forming rod 2 is slowly moved horizontally to one side by the action of air blown from the cold roller 12 a.

The forming rod 2 functions as a collector in the first and second melt spinning devices 6 and 10 and also functions as a collector in the electrospinning device 8. For this purpose, the forming rod is made of a conductive material and is grounded at one end thereof. Also, the forming rod 2 has a smooth surface such that the fiber layer formed on the forming rod 2 can be moved horizontally to one side.

The forming rod 2 is rotated under the control of the driving unit 4 at a revolution speed at which it can receive both a fiber from the first and second melt spinning devices 6 and 10 and a fiber from the electrospinning device 8. Preferably, the forming rod is rotated at a low speed of 30-50 rpm. If it is required to further increase the production rate of the filter, the revolution speed of the forming speed 2 in the operation of the first and second melt-spinning devices 6 and 10 may be increased relative to the revolution speed of the forming speed 2 in the operation of the electrospinning device 8.

The first and second melt spinning devices 6 and 10 are devices of melt-spinning micrometer-sized fiber yarns using an air-blowing process, and the electrospinning device is a device of electrospinning nanometer-sized fiber yarns. Although the second melt-spinning device 10 melt-spins micrometer-sized fiber yarns, like the first melt-spinning device 6, it is preferably structured such that it spins fiber yarns having a diameter larger than that of fiber yarns spun from the first melt-spinning device.

The electrospinning device 8 comprises a syringe pump including a syringe having a metal syringe needle spinneret, a collector unit, which is composed of the forming rod 2 and grounded at one end thereof, and a high-voltage power supply for applying a high-voltage electric field of 0-40 V to the syringe pump and the collector unit. In the electrospinning device 8, a positively charged polymer solution is drawn and spun by an electric field applied from the metal syringe needle spinneret to the forming rod 2 as the collector unit so as to form a nanofiber layer on the forming rod 2.

At positions opposite the first melt-spinning device 6 and the electrospinning device 8, the cold rollers 12 a and 12 b are provided such that they are rotated in contact with the forming rod 2. It functions to press the surface of a fiber layer formed on the forming rod 2 at a constant pressure so as to make the fiber layer dense and uniform, and also functions to cool the fiber layer by air blowing. Particularly, among the cold rollers 12 a and 12 b, the cold roller 12 a opposite the first melt-spinning device 6 consists of a tapered bobbin such that, when fiber layers formed on the forming rod 2 get loose due to the projection of the piece received in the forming rod 2, the cold roller 21 a will blow air in an inclined direction, so that the fiber layers will be pushed and slowly moved horizontally. The cold roller 12 b is a cylinder-shaped roller.

As a plurality of fiber layers formed on the forming rod 2 continues to be pushed and moved to the cutter unit 14, a cutter in the cutter unit 14 cuts the fiber layers to a predetermined effective length, thus providing a cylindrical composite fiber filter 200 as shown in FIG. 2.

The control unit of the composite fiber filter-manufacturing apparatus 100 controls the driving unit 4 to rotate the forming rod 2 at a predetermined revolution speed of 30-50 rpm, and first operates the first melt-spinning device 6 so as to spin microfiber yarns onto the forming rod 2, thus forming an inner fiber layer 20 as shown in FIG. 2. At this time, the cold roller 12 a rotates in contact with the forming rod 2 while it presses the inner microfiber layer 20 being formed.

As the inner microfiber layer 20 is formed to a predetermined thickness, the control unit controls the driving unit 4 to allow the piece received in the forming rod 2 to project outward, such that the inner microfiber layer 20 being formed gets slightly loose. Accordingly, the inner microfiber layer 20 formed on the forming rod 2 is slowly moved horizontally to one side by the action of air blown inclinedly from the tapered cold roller 12 a. At this time, the first melt-spinning device 6 continues to spin microfiber yarns, and the electrospinning device 8 and the second melt-spinning device 10 start to operate under the control of the control unit, thus performing electrospinning and melt-spinning.

By electrospinning by the electrospinning device 8 and melt-spinning by the second melt-spinning device 10, as shown in FIG. 2, a nanofiber layer 22 and an outer microfiber layer 20 are sequentially deposited on the inner microfiber layer 22. As the cylindrical multilayer fiber structure formed on the forming rod 2 is slowly moved horizontally to enter the cutter unit 14, a cutter in the cutter unit 14 cuts the cylindrical structure to an effective length, thus manufacturing a cylindrical composite fiber filter 200 as shown in FIG. 2.

Although the embodiment of manufacturing the cylindrical composite fiber filter 200 using two melt-spinning devices and one electrospinning device in the inventive composite fiber filter-manufacturing apparatus has been described, it will be apparent to those skilled in the art that, like an embodiment shown in FIG. 3, the microfiber layer 20 and the nanofiber layer 22 may also be alternately deposited in a plurality of layers.

Particularly, in the embodiments shown in FIGS. 2 and 3, the diameter of the nanofiber yarns constituting the nanofiber 22 is in the range of a few nanometers (nm) to a few hundreds of nanometers (nm), and preferably 50-800 nm. Because such nanofiber yarns are very thin, they have large surface and high flexibility, such that they can be easily processed by pressing and can be suitably applied as materials for filters. Therefore, the nanofiber layer 22 consisting of nanofibers has numerous pores, and thus can filter out almost all fine particles under low pressure.

The thickness of the nanofiber layer 22 according to the embodiment of the present invention may be determined within the range of a few nanometers to a few hundreds of nanometers in consideration of the filter efficiency of the relevant filter by filter manufacturers.

Also, the nanofiber layer 22 according to the embodiment of the present invention, when used for water purification filters, preferably has an average pore size of 1-3.5 μm, a porosity of 30-70%, a pure density of 0.1-0.22 g/cm³ and an apparent density of 0.18-0.35 g/cm³.

In order to use a combination of microfiber technology and nonofiber manufacturing technology to realize a functional filter, which has a competitive price, solves problems of differential pressure and filtration efficiency, secures high efficiency and high functionality and also have antibacterial activity, the following raw materials and various spinning parameters are required in the present invention.

The microfiber layer 20 is made of synthetic resin, which is melt-spinnable in a melt-spinning device, and examples of the synthetic resin include polypropylene (PP), polyethylene terephthalate, polyvinylidene fluoride, nylon, polyvinyl acetate, polymethyl methacrylate, polyacrylonitrile, polyurethane, polybutylene terephthalate, polyvinyl butyral, polyvinyl chloride, polyethyleneimine, polysulfone, polyolefin and the like, preferred being polypropylene (PP).

Also, the nanofiber layer 22 is preferably made of polymer resin having a given dielectric constant which allows the polymer resin material to be electrospun.

Examples of the polymer resin, which constitutes the nanofiber layer 22 and has a given dielectric constant, include polymer resins soluble in organic solvents, including water, preferred being polyacrylonitrile (PAN) resin or polyamide (nylon 6).

Other examples of the polymer resins soluble in organic solvents, including water, include polyvinyl alcohol, polystyrene, polycaprolactone, polyethylene terephthalate, polyvinylidene fluoride, nylon, polyvinyl acetate, polymethyl methacrylate, polyacrylonitrile, polyurethane, polybutylene terephthalate, polyvinyl butyral, polyvinyl chloride, polyethyleneimine, polysulfone, nitrocellulose and the like. Among them, polystyrene, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyurethane, polyvinyl butyral, polyvinyl chloride, polysulfone, nitrocellulose and the like have good water resistance and chemical resistance (alkaline resistance, acidic resistance, etc.), and thus can preferably be applied to form the nanofiber layer 22 for water purification filters.

Moreover, in forming the microfiber layer 20 and the nanofiber layer 22, silver nanoparticles are also added in the embodiment of the present invention in order to secure high efficiency and high functionality and to impart antibacterial activity. For this purpose, chips made of polypropylene are added and melted in the melt-spinning device for the melting of microfiber yarns, and in the embodiment of the present invention, silver nanoparticles are added to the polypropylene chips. The silver nanoparticles are melted at a temperature much lower than the melting temperature of the polypropylene chips.

Also, to electrospin nanofiber yarns, silver nanoparticles are added to the polymer resin solution in the syringe. It is very important to disperse and distribute silver nanoparticles when they are mixed in the melt-spinning device and the syringe, and for this purpose, a solvent such as alcohol should be added. However, a solvent such as alcohol causes partial precipitation of silver particles, and for this reason, silver nanoparticles, which can be dispersed and distributed without needing a solvent such as alcohol, are used in the embodiment of the present invention. The silver nanoparticles are dispersed by themselves.

If a solvent used to disperse silver nanoparticles is alcohol as in the prior art, the content of silver will be only about 0.1 wt % relative to the weight of the polymer resin, and thus will show insufficient antibacterial activity. If silver particles are added in an amount much larger than 0.1 wt % in order to increase antibacterial activity, the precipitation thereof will occur.

However, silver nanoparticles having self-dispersing ability, as used in the embodiment of the present invention, may be added in an amount up to 1 wt % based on the weight of the polymer resin, and the addition of silver nanoparticles in an amount larger than 1 wt % will not show any additional effect. This is because, even when silver nanoparticles are added in an amount of 0.5 wt % based on the weight of the polymer resin, they will show a growth inhibition rate close to 100%.

Thus, the silver nanoparticles having self-dispersing ability, which are used in the embodiment of the present invention, are preferably added in an amount of 0.1-1.0 wt %, and more preferably 0.3-0.6 wt %, based on the weight of the polymer resin.

The addition of silver nanoparticles for imparting antibacterial activity may be applied to both microfiber yarns and nanofiber yarns in the above-specified mixing ratio. If necessary, the addition of silver nanoparticles may also be applied only to either microfiber yarns or nanofiber yarns, and in this case, it is applied to the nanofibers having a relatively high surface area and porosity.

In order for the composite fiber filter to sufficiently the function thereof, it is important that fiber yarns for forming the microfiber layer 20 and the nanofiber layer 22 can be made uniform and as thin as possible.

In forming the microfiber layer 20, the diameter of spinning nozzles, spinning temperature and spinning distance in the melt-spinning devices 6 and 10 should be considered in order to make polypropylene microfiber yarns uniform and to spin the yarns to a thickness smaller than that of the prior art. The present inventors have established the optimal melt-spinning conditions by performing experiments at various melt-spinning conditions.

The present inventors performed an experiment for using the cylindrical composite fiber filter 200 as a water purification filter. For the use of the composite fiber filter as a water purification filter, it is preferable that the composite fiber filter should have strength capable of withstanding pressure applied in water purification operations and, at the same time, the average diameter thereof should be uniform.

It was found that, among the parameters which are considered to realize the water purification filter, the spinning temperature is preferably 280-300° C., and the spinning distance is not a parameter required for securing the uniformity of microfibers.

However, it was found that the diameter of spinning nozzles is a very important parameter required for securing the uniformity of microfibers. Herein, it was found that the diameter of spinning nozzles is preferably 0.1-0.3 mm, and a lower value in the range of 0.1-0.3 mm is more advantageous in securing the uniformity of microfibers.

In one experiment, melt spinning was performed at a spinning nozzle diameter of 0.2 mm while the spinning distance was slightly changed for each melt spinning. As a result, uniform microfibers having an average diameter of 12-17 μm could be obtained. In this case, it could be found that an increase in the spinning distance led to a decrease in the diameter of the microfiber yarns, and it would be preferable to reduce the spinning distance in order to optimize production efficiency. For example, the spinning distance is in the range of about 80-230 mm.

According to the embodiment of the present invention, microfiber yarns of forming the microfiber layer 20 can be made uniform while they have an average diameter of 12-17 μm. Thus, these microfiber yarns have advantages in that they are much thinner than the general diameter of microfiber yarns forming the prior water purification filter, for example, 23-50 μm, and thus have larger surface area and high flexibility, compared to the prior art.

Then, in forming the nanofiber layer 22 according to the embodiment of the present invention, parameters for electrospinning in the electrospinning device 8 should be considered in order to uniformly spin nanofiber yarns made of polymer resin having a given dielectric constant and to increase reproducibility. The parameters include voltage, spinning distance, spinning rate, polymer resin solution concentration, etc.

In the embodiment of the present invention, N,N-dimethylfomatmide (DMF) was used as a solvent to dissolve polyacrylonitrile (PAN) resin among polyacrylonitrile (PAN) resin and polyamide (nylon 6), which are preferred examples of polymer resin having a given dielectric constant. Also, formic acid was used as a solvent to dissolve polyamide (nylon 6).

The present inventors performed a nanofiber formation experiment for applying the cylindrical composite fiber filter 200 as a water purification filter. The experiment was performed for the cases where polyacrylonitrile resin was used as polymer resin to form the nanofiber layer 22 of a water purification filter and where polyamide (nylon 6) was used as the polymer resin.

First, the experiment for the case where the polymer resin is polyacrylonitrile resin will now be described.

The polyacrylonitrile resin (PAN) resin was dissolved in the N,N-dimethylformamide (DMF) solvent to form a PAN/DMF solution (polymer solution). It could be seen through the experiment that important parameters to be considered in electrospinning the PAN/DMF solution are the concentration of the polymer resin in the PAN/DMF solution, the spinning rate of the PAN/DMF solution, application voltage, spinning distance, etc.

In this case, the diameter of the resulting nanofibers showed a tendency to decrease with a decrease in the concentration of the polymer resin in the solution and the spinning rate of the solution, and showed a tendency to decrease with an increase in application voltage and spinning distance.

Examples of nanofibers, which are optimal for use in water purification filters, are as follows:

(1) PAN Nanofibers having Average Diameter of 600 nm

These PAN nanofibers were obtained under the following electrospinning conditions: the concentration of the polymer resin in the solution: 12 wt %, the sinning rate of the solution: 1.2 ml/hr, application voltage: 15 kV, and spinning distance: 15 cm.

(2) PAN Nanofibers having Average Diameter of 600 nm

These PAN nanofibers were obtained under the following electrospinning conditions: the concentration of the polymer resin in the solution: 10 wt %, the sinning rate of the solution: 1.2 ml/hr, application voltage: 15 kV, and spinning distance: 13 cm.

Among the optimized PAN nanofibers, the PAN nanofiners having an average diameter of about 300 nm have advantages in that they have a uniform shape, no beads, and excellent reproducibility. Moreover, a sheet made of the PAN nanofibers having an average diameter of about 600 nm is simple to operate, the thickness thereof is simple to control, and thus the sheet is most preferably applied to the nano/micro composite fiber filter. Also, the PAN nanofibers may also be easily applied in carbon nanofiber-manufacturing processes and the like.

The experiment for the case where the polymer resin is polyamide (nylon 6) will now be described.

Polyamide (nylon 6) was dissolved in a formic acid solvent to make a polymer solution, which was then electrospun under various conditions. As a result, it was found that highly reproducible and uniform nanofibers were obtained in the following electrospinning conditions: voltage: 10-19 kV, spinning distance: 8-20 cm, spinning rate: 0.1-0.3 ml/hr, and the concentration of the polymer in the solution: 15-26 wt %.

By electrospinning in the above-described electrospinning conditions, polyamide (nylon 6) nanofibers having an average diameter of about 200 nm could be manufactured.

In the embodiment of the present invention, silver nanoparticles were added before spinning in order to impart antibacterial activity to the microfiber layer 20 and the nanofiber layer 22.

Whether the spinning of the fiber yarns having silver nanoparticles added thereto is properly achieved should be confirmed, and even when the spinning of the fiber yarns is properly achieved, whether the resulting fiber yarns have antibacterial activity should be confirmed.

In one embodiment, the present inventors could manufacture antibacterial nanofibers by adding silver nanoparticles having a particle size of 10-20 nm to polyamide (nylon 6) and electrospinning the polymer. Through experiments, it was found that the thickness of the nanofiber yarns was decreased with an increase in the application voltage of the electrospinning device, and the change in the concentration of silver nanoparticles did not lead to the change in the shape of the nanofibers.

Then, an experiment was performed to examine whether the manufactured polyamide (nylon 6)/silver nanofiber yarn nonwoven fabric would contain a silver component and show antibacterial activity.

FIGS. 4 a and 4 b show TEM analysis images for polyamide (nylon 6)/silver nanofiber yarns, and FIG. 5 shows an EDS (Energy Dispersive Spectroscopy) analysis image for polyamide (nylon 6)/silver nanofiber yarns. Referring to FIGS. 4 a and 4 b, it can be seen that silver nanoparticles having a size of 10-20 nm are dispersed into the surface and inside of the polyamide (nylon 6)/silver (Ag) nanofiber yarns. Also, from the peak of silver (Ag) in FIG. 5, it can be seen that the nanofiber yarns contain silver (Ag).

The present inventors performed antibacterial tests using Staphylococcus aurus and Klebsiella pneumonia. Staphylococcus aurus is one example of positive bacteria, and Klebsiella pneumonia is one example of negative bacteria.

FIGS. 6 a is a bar graph showing the results of antibacterial activity tests conducted using Staphylococcus aurus, and FIGS. 6 b is a bar graph showing the results of antibacterial activity tests conducted using Klebsiella pneumonia.

Referring to the graphs in FIGS. 6 a and 6 b, it can be seen that, in the antibacterial tests, a silver content higher than 1000 ppm showed a growth inhibition rate higher than 90%. Herein, the growth inhibition rate (%) is calculated according to the following equation: (A−B/A)×100, wherein A is the number of viable cells cultured in a general nonwoven fabric, and B is the number of viable cells cultured in the silver-containing nanofiber nonwoven fabric. The silver content of 1000 ppm is a value corresponding to about 0.3 wt % relative to the weight of the polymer resin.

A growth inhibition rate of about 20-30% is regarded as an insignificant antibacterial effect, and a growth inhibition rate higher than 90% is regarded as a very good antibacterial effect. Therefore, it can be seen that the silver-containing nanofiber nonwoven fabric of the present invention shows a high antibacterial effect when the silver content thereof is higher than 1000 ppm.

FIGS. 7 a and 7 b show the results of antibacterial zone tests conducted using Staphylococcus aurus and Klebsiella pneumonia. Specifically, FIG. 7 a is a photograph showing the result of an antibacterial zone test conducted using Staphylococcus aurus, and FIG. 7 b is a photograph showing the result of an antibacterial zone test conducted using Klebsiella pneumonia. In FIGS. 7 a and 7 b, the sample nonwoven fabric marked by “N” is a general nanofiber nonwoven fabric (left), and the sample nonwoven fabric having no mark (right) is a silver-containing nanofiber nonwoven fabric containing about 1500 ppm of silver.

As can be seen in FIGS. 7 a and 7 b, the bacteria could not inhibit and proliferate on and around the silver nanoparticle-containing nonwoven fabric (right).

FIG. 8 is an SEM image photograph showing that the nanofiber layer 22 formed on the microfiber layer 20 by electrospinning of nanofibers according to an embodiment of the present invention, and FIGS. 9 a to 9 c are SEM image photographs of partial cross-sections, showing that the nanofiber layer 22 and the outer microfiber layer 20 are sequentially deposited on the inner microfiber layer 20.

The present inventors tested filtration efficiency as a function of particle size using the prior microfilter and the cylindrical composite fiber filter 200 constructed as shown in FIG. 2. The test results are shown in FIGS. 10 a and 10 b.

In a table of FIG. 10 a and a graph of FIG. 10 b, “Daejin micro filter” is the prior microfilter, and “Daejin nano filter” is a sample of the cylindrical composite fiber filter 200 as shown in FIG. 2. By comparison, it can be seen that “Daejin nano filter” that is the sample of the cylindrical composite fiber filter 200 has a filtration efficiency of more than about 99% even for particles having a size of 0.1 μm, whereas “Daejin micro filter” that is the prior microfilter has a filtration efficiency of only about 80% even for particles having a size larger than 3 μm.

The results of such comparison demonstrate that the cylindrical composite fiber filter 200 according to the embodiment of the present invention has very excellent filtration efficiency.

Furthermore, the present inventors tested pressure loss as a function of flow rate in the prior microfilter and the cylindrical composite fiber filter 200 constructed as shown in FIG. 2, and the test results are shown in FIGS. 11 a and 11 b. The pressure loss means the difference between the pressure of flow entering the filters and the pressure of flow discharged from the filters, and a lower pressure loss is more preferable.

Referring to FIGS. 11 a and 11 b, it can be seen that, at a flow rate of 12-18 l/min, pressure loss as a function of flow rate is not significantly different between the prior microfilter (Daejin micro filter) and the composite fiber filter (Daejin nano filter) of the present invention. Particularly, general service water has a flow rate of about 12 l/min, and at this flow rate, pressure loss in “Daejin micro filter” is 0.015, and differential pressure in the composite fiber filter (Daejin nano filter) of the present invention 0.021.

Therefore, the composite fiber filter of the present invention shows a differential pressure almost similar to that in the general microfilter in the case of general service water, and thus is considered to have very good performance. In consideration of the fact that the differential pressure of a reverse osmosis-type filter in general service water a several tens of liters/min, it can be understood that the composite fiber filter of the present invention has greatly improved differential pressure performance.

The cylindrical composite fiber filter according to the embodiment of the present invention may also be developed in the form of a planar composite fiber filter by incising it lengthwise.

It will be obvious to those skilled in the art that the composite fiber filter of the present invention can be applied not only in water purification applications, but also for air cleaning and other applications.

While the present invention has been described with respect to the preferred embodiment thereof, various modifications are possible without departing from the scope of the present invention.

For example, in an embodiment alternative to the above-described embodiment of manufacturing the composite fiber filter by combining the microfiber nonwoven fabric with the nanofibers using the continuous process, the composite fiber filter may also be manufactured by producing a large amount of a planar nanofiber nonwoven fabric in a separate process, winding the nanofiber nonwoven fabric on the mocrofiber layer 20 formed on the forming rod of FIG. 1, to a given thickness, and then depositing the microfiber layer on the nanofiber layer using the microfiber melt-spinning device of FIG. 1.

In this case, the forming rod 2 does not need necessarily to be made of a conductive material, nanofibers forming the planar nanofiber nonwoven fabric, which is separately produced, contain self-dispersing silver nanoparticles to the polymer resin in an amount of 0.1-1.0 wt % based on the weight of the polymer resin, and the planar nanofiber nonwoven fabric is preferably manufactured to have a porosity of 30-70% and a density of 0.1-0.22 g/cm³.

In another embodiment of the present invention, a nanocomposite fiber filter for water purification may also be manufactured by laminating the nanofiber nonwoven fabric of the present invention on a microfiber nonwoven fabric such as a spunbond fabric using an electrospinning process, and then winding the resulting fiber structure cylindrically to a given thickness. In this case, nanofibers forming the nanofiber nonwoven fabric contain self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of the polymer resin, and the nanofiber nonwoven fabric is formed to have a porosity of 30-70% and a density of 0.1-0.22 g/cm³.

In addition, according to the present invention, a folded cylindrical nanocomposite fiber filter may also be manufactured by stacking the planar nanofiber nonwoven fabrics alternately with the microfiber nonwoven fabrics to form a multilayer structure, and bending the multilayer structure. In this case, nanofibers forming the nanofiber nonwoven fabric contain self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of the polymer resin, and the nanofiber nonwoven fabric has a porosity of 30-70% and a density of 0.1-0.22 g/cm³.

Accordingly, the scope of the present invention is not determined by the above-described embodiments, but rather is to be determined by the appended claims and their equivalents.

As described above, according to the present invention, the composite fiber filter having high efficiency, high functionality and antibacterial activity can be realized by combining nanofibers with microfibers and can be used in water purification filter applications and other applications.

Although the preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

1. A method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is made of a conductive material, grounded at one end thereof and rotatably driven, using a melt-spinning device, so as to form on the forming layer a microfiber layer consisting of the microfiber yarns; and electrospinning an electrospinnable polymer solution having a given dielectric constant, on the microfiber layer, using an electrospinning device, so as to form on the microfiber layer a nanofiber layer consisting of nanofiber yarns.
 2. The method of claim 1, wherein the microfiber layer and the nanofiber layer are alternately and sequentially deposited on each other using the melt-spinning device and the electrospinning device so as to form a multilayer structure.
 3. The method of claim 1, wherein the polymer resin solution contains self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of the polymer resin.
 4. The method of claim 1, wherein the nanofiber layer has a porosity of 30-70% and a density of 0.1-0.22 g/cm³.
 5. The method of claim 1, wherein the polymer resin contained in the nanofiber yarns is polyacrylonitrile resin or polyamide (nylon 6).
 6. The method of claim 1, wherein the polymer resin contained in the nanofiber yarns is any one selected from the group consisting of polyvinyl alcohol, polystyrene, polycaprolactone, polyethylene terephthalate, polyvinylidene fluoride, nylon, polyvinyl acetate, polymethyl methacrylate, polyacrylonitrile, polyurethane, polybutylene terephthalate, polyvinyl butyral, polyvinyl chloride, polyethyleneimine, polysulfone and nitrocellulose.
 7. The method of claim 1, wherein the microfiber yarns being melt-spun comprise polypropylene and contain self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of the polypropylene.
 8. The method of claim 1, wherein the forming rod is rotatably driven at a revolution speed of 30-50 rpm.
 9. The method of claim 1, wherein the melt-spinning device has a spinning nozzle diameter of 0.1-0.3 mm and a spinning distance of 80-230 mm.
 10. The method of claim 1, wherein electrospinning parameters in the electrospinning device include the concentration of the polymer resin in the polymer resin solution, the spinning rate of the polymer resin solution, application voltage and spinning distance.
 11. The method of claim 10, wherein the electrospinning parameters in the electrospinning device further include silver concentration.
 12. The composite fiber filter manufactured according to a method set forth in claim
 1. 13. A method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is made of a conductive material, grounded at one end thereof and rotatably driven, using a first melt-spinning device, so as to form on the forming rod a first microfiber layer consisting of first microfiber yarns; electrospinning an electrospinnable polymer resin having a given dielectric constant, on the microfiber layer, using an electrospinning device, so as to form on the microfiber layer a nanofiber layer consisting of nanofibers; and melt-spinning microfiber yarns on the nanofiber layer using a second melt-spinning device, so as to form on the nanofiber layer a second microfiber layer consisting of second microfiber yarns having a diameter different from that of the first microfiber yarns, wherein the fiber layers are sequentially deposited on the forming rod.
 14. An apparatus for manufacturing a composite fiber filter using nanofibers, the apparatus comprising: a forming rod, which is made of a conductive material and grounded at one end thereof and can be rotatably driven by a driving unit; and one or more melt-spinning devices and electro-spinning devices, which are provided in the vicinity of the forming rod, whereby a microfiber layer consisting of microfiber yarns and a nanofiber layer consisting of nanofiber yarns are alternately and sequentially deposited on the forming rod by melt-spinning from the melt-spinning devices and electrospinning from the electrospinning devices.
 15. The apparatus of claim 14, wherein a cold roller is provided at a position opposite each of the melt-spinning devices and the electrospinning devices, such that it is rotated to press the forming rod.
 16. The apparatus of claim 14, further comprising a cutter for cutting the cylindrical fiber layers, which are alternately and sequentially deposited on the forming rod, to a predetermined effective length.
 17. A method for manufacturing a composite fiber filter using nanofibers, the method comprising: melt-spinning microfiber yarns on a forming rod, which is rotatably driven, using a first melt-spinning device, so as to form on the forming rod a first microfiber layer consisting of first microfiber yarns; winding on the first microfiber layer a planar nanofiber nonwoven fabric consisting of nanofiber yarns, which contain silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin, to a given thickness, so as to form on the microfiber layer a nanofiber layer; and melt-spinning microfiber yarns on the nanofiber layer using a second melt-spinning device, so as to form on the nanofiber layer a second microfiber layer consisting of second microfiber yarns having a diameter different from that of the first microfiber yarns, wherein the fiber layers are sequentially deposited on the forming rod.
 18. A method for manufacturing a composite fiber filter using nanofibers, the method comprising: laminating a nanofiber nonwoven fabric on a microfiber nonwoven fabric using an electrospinning process, and then winding the resulting fabric structure in the form of a cylinder to a given thickness so as to manufacture a nanocomposite fiber filter for water purification, wherein nanofibers forming the nanofiber nonwoven fabric contain self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin, and the nanofiber nonwoven fabric has a porosity of 30-70% and a density of 0.1-0.22 g/cm³.
 19. A method for manufacturing a composite fiber filter using nanofibers, the method comprising: stacking planar nanofiber nonwoven fabrics alternately with planar microfiber nonwoven fabrics to form a multilayer structure, and then bending the multilayer structure to form a folded cylindrical nanocomposite fiber filter, wherein the nanofiber nonwoven fabric consists of nanofibers containing self-dispersing silver nanoparticles in an amount of 0.1-1.0 wt % based on the weight of polymer resin and has a porosity of 30-70% and a density of 0.1-0.22 g/cm³. 